Technique for encoding digital information in a carrier wave

ABSTRACT

A method for redeeming a coupon using a mobile device is disclosed. The method comprises allowing a user to select the coupon; accessing at least one melody stored in a memory of the mobile device; passing a coupon identifier for the coupon and the at least one melody to an encoder component of the mobile device encoding the coupon identifier and the melody by the encoder component to generate a signal for transmission; and transmitting said signal through a speaker of said mobile device for reception through a microphone of a receiving mobile device.

This application claims that the benefit of priority to prior U.S.provisional patent application No. 61/993,965 entitled “TECHNIQUE FORENCODING DIGITAL INFORMATION IN A CARRIER WAVE”, filed May 15, 2014.

BACKGROUND

Embodiments of the invention relate to techniques for encoding digitalinformation in a carrier wave.

Coupons are routinely published by merchants/vendors in order to improvesales. Historically, coupons existed in printed form. However,increasingly coupons now exist in digital form wherein they may beviewed on display screen of a device such as a tablet computer.

SUMMARY

In one aspect of the invention, a novel encoding scheme for transmittingdigital data over a short-range audio link is disclosed. Advantageously,for the transmission commodity microphone and speaker hardwareassociated with a handheld mobile device may be used. Moreover, evenunder noisy conditions the digital data may transmitted and decoded.

In another aspect of the invention, the encoding scheme may be designedto spread signal energy over a wide frequency range to provide immunityagainst frequency-dependent channel fades. Simultaneously, the schememay allow for complexity detection of incoming transmissions, as well asprecise synchronization to the digital data stream encoded in thetransmission.

In another aspect of the invention, the encoding scheme may be designedto make maximum use of the limited dynamic range of the transmit speakerhardware by using square wave rather than sinusoidal signals.

As implemented, the invention may have the usual elements of anycommunication system including a source encoder or compression engine,an error correction code, a checksum sequence, digital to analogconverter and transducer hardware to create sound waves from a voltagewaveform on the transmitter side, and a sensor e.g. a microphone todetect air pressure variations from sound waves, an analog to digitalconverter, logic to detect and decode incoming data transmissions and tocheck the integrity of the transmission using the checksum.

The transmitted waveform may comprise a concatenation of two or more ofthe following distinct signals: a “start melody”, “detection beacon”,“preamble”, “silence gaps”, “data” and “end melody”.

Each of these signals are intended to serve one distinct purpose: e.g.the start and end “melodies” are designed to bookend the rest of thetransmission to make the overall audio pleasing or at least comfortableto the human ear. It may also have the effect of masking thetransmission to potential eavesdropping devices.

In another aspect of the invention, two or more separate signals may begenerated to aid detection and synchronization. In conventionalcommunications systems, a preamble sequence which has sharply peakedautocorrelation properties is used to accurately identify the start ofincoming transmissions. However, detecting such a sequence requires theuse of a linear filter matched to the preamble sequence which usuallytakes the form of an FIR filter with a long impulse response. This canbe an expensive operation in terms of power, CPU and memory especiallyfor receivers that need to continuously monitor for incomingtransmissions. A device using the inventive encoding scheme may employan additional signal that is easy to detect, but does not have a sharpcorrelation function to first detect a transmission and only then invokethe expensive filter that searches for the preamble.

The waveform used to modulate data may have a constant envelope or atleast a small peak to average ratio (e.g. the peak to average powerratio may be 0.5). One example of such a signal is a “square chirp(SC)”; just like the common chirp signal, the SC is a quasi-periodicsignal with a frequency that increases at a constant rate in time over aspecified band. However, unlike the common (sinusoidal) chirp, the SCconsists of square waves, which surprisingly makes better use of thepeak transmit power capability of the speaker hardware. The use ofsquare wave signals in SC does lead to higher frequency harmonics, butunder peak power rather than battery constraints, thus the waste ofpower represented by these harmonics is irrelevant. In one embodiment,interference with other devices is not an important considerationbecause of the short range and short duration of the transmission.

Other aspects of the invention will be apparent from the detaileddescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a deployment drawing, in accordance with one embodiment ofthe invention

FIG. 2 shows the use cases for the DCPMS, in accordance with oneembodiment of the invention.

FIG. 3 shows the use cases for coupon generation, in accordance with oneembodiment of the invention.

FIG. 4 shows the use cases for coupon clipping and publishing inaccordance with one embodiment of the invention.

FIG. 5 shows a coupon query Q1, in accordance with one embodiment of theinvention.

FIG. 6 shows the use cases for the customer coupon app, in accordancewith one embodiment of the invention.

FIGS. 7a-b shows a Publisher publishing media on a Customer node, inaccordance with one embodiment of the invention.

FIG. 8 shows a flowchart for processing a coupon clipping notification,in accordance with one embodiment of the invention.

FIG. 9A shows the use cases for coupon redemption by the customer couponapp, in accordance with one embodiment of the invention.

FIG. 9B shows the use cases for coupon redemption by the retailer couponapp, in accordance with one embodiment of the invention.

FIG. 10 shows an example of published coupon, in accordance with oneembodiment of the invention.

FIG. 11 shows the published coupon of FIG. 10 in magnified view, inaccordance with one embodiment of the invention.

FIG. 12 shows an example of a report to an Advertiser, in accordancewith one embodiment of the invention.

FIG. 13 shows a high-level block diagram of hardware for implementingthe DCPMS, in accordance with one embodiment of the invention.

FIG. 14 shows a transmitting device A and receiving device B configuredto perform the encoding scheme of the present invention.

FIG. 15 shows a code 14, representing a coupon sandwiched between afirst part 10 of a melody and a second part 12 of said melody, inaccordance with one embodiment of the invention.

FIG. 16 of the drawings illustrates how a coupon code may be encodedinto a signal using the encoding scheme of the present invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the invention. It will be apparent, however, to oneskilled in the art that the invention can be practiced without thesespecific details. In other instances, structures and devices are shownin block diagram form only in order to avoid obscuring the invention.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The appearance of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not other embodiments.

Moreover, although the following description contains many specifics forthe purposes of illustration, anyone skilled in the art will appreciatethat many variations and/or alterations to said details are within thescope of the present invention. Similarly, although many of the featuresof the present invention are described in terms of each other, or inconjunction with each other, one skilled in the art will appreciate thatmany of these features can be provided independently of other features.Accordingly, this description of the invention is set forth without anyloss of generality to, and without imposing limitations upon, theinvention.

Broadly, embodiments of the invention disclose an encoding scheme fortransmitting digital data over a short-range audio link. Advantageously,for the transmission commodity microphone and speaker hardwareassociated with a handheld mobile device may be used. Moreover, evenunder noisy conditions the digital data may transmitted and decoded.

The encoding scheme may be used to facilitate the redemption or exchangeof coupons in digital form, as will be described later.

Referring to FIG. 14 of the drawings, there is shown a transmittingdevice A, and receiving device B. The device A may be a mobile phone,tablet computer, or any other like consumer device which includes adisplay screen by which a coupon may be viewed. The device B may besimilar to the device A in functionality, and may represent a deviceunder control of a merchant.

In one use case, a coupon loaded into a memory associated with thedevice A is to be redeemed by transmission of said coupon from thedevice A to the device B, as will be described.

In one embodiment, a code representing the coupon on the device A may beencoded for transmission by a carrier wave using a frequency modulationscheme such as Frequency-Shift Keying (FSK). Thus, the coupon may betransmitted using discreet frequency changes of a carrier wave that isbroadcast from the device A to device B.

Unfortunately, said discreet frequency changes when heard by the humanear can be very unpleasant. Accordingly, in one embodiment, the coderepresenting the coupon is sandwiched between two portions of themelody/tune, which are also encoded through frequency modulation fortransmission by the carrier wave. This is shown in FIG. 15 of thedrawings, where a code 1504, representing the coupon is sandwichedbetween a first part 1500 of a melody and a second part 1502 of saidmelody.

Referring now the FIG. 16 of the drawings, in one embodiment, in orderto generate a signal with a coupon code sandwiched between two parts ofthe melody, a coupon 1600 is input into an encoder 1602. The encoder1602 is configured to implement encoding techniques, such as the FSKencoding technique described above. The encoder 1602 encodes the coupon1600 together with a melody or tune to produce a sound file 1604 whichincludes two melody portions and a code representing the coupon 1600sandwiched therebetween in similar fashion to what has been describedabove with reference to FIG. 15. The encoding and the generation of thesound file 1604 is performed by the device A.

In one embodiment, for exchange or redemption of coupon, the device Aplays the sound file 1604 at block 1606. The sound file 1604 is receivedby the device B at block 24 through a microphone associated with thedevice B. Within the device B, once the code portion 1504 of the soundfile 1604 has been received, decoding thereof begins. This processhappens concurrently as the melody portions 1500/1502 are played. In oneembodiment, the melody portions 1500/1502 may be of a sufficient lengthto enable the device B to completely decode the portion 1504 so thatwhen the melody portions 1500/1502 end, the code 1504 is completelydecoded. Thus, a perception of a fast decode is achieved. Moreover,playing of the melody portions masks the unpleasant sound associated tothe code 1504.

FIG. 1 shows a deployment scenario 100 for a coupon service, inaccordance with one embodiment of the invention. Referring to FIG. 1 aDigital Coupon Personalization and Management System (DCPMS) 102includes a server component 102A which implements a Coupon Service (CS)102B. The CS 102B is under control of a Coupon Service Provider (CSP) Aplurality of advertiser nodes 104 each equipped with an appropriate useragent (browser) 104A are communicatively coupled to the DCPMS 102 bymeans of a network link 112. In one embodiment, each advertiser node 104may include a computing device such as a laptop or PC, and the networklink 112 may comprise the Internet. Each advertiser node 104 representan Advertiser who uses the CS to generate coupons on its behalf, as willbe explained.

The DCPMS 102 may also be communicatively coupled with plurality ofpublisher nodes 106 by means of a network link 112. Each publisher node106 represent a computing device such as a PC and includes a publishinginterface 106A, which represent the mechanism whereby a Publisher isable to publish media on a customer node 108 for viewing by a Customer.Examples of Publishers includes CNN, Facebook, YouTube, etc.

The customer node 108 represents a customer device such as smartphone ortablet PC. In one embodiment, the customer node 108 may include apublisher app 108A and a coupon app 108B. The publisher app 108A may beconfigured to receive media content from a Publisher, as will bedescribed more fully later. The media content may include a personalizedcoupon generated by the DCPMS 102.

Finally, the deployment scenario 100 also includes a retailer node 110which represents retailer. In one embodiment, the customer node 108communicates with the retailer node 110 via an audio link 114.

FIG. 2 shows use cases 200 for the DCPMS 102, in accordance with oneembodiment of the invention. As will be seen, the DCPMS 102 supports acreate_account( ) function 202 which allows an Advertiser and aPublisher to create user accounts on the DCPMS 102. Aconfigure_business_rules( ) function 208 allows an Advertiser toprovision business rules and objectives in the DCPMS 102. The businessrules and objectives may be used to generate highly personalized couponsfor publishing to particular customers, as will be described. The usecases 200 also includes a configure_coupon_generation_parameters( )process 210 whereby an advertiser configures coupon generationparameters which are used to generate personalized coupons. Examples ofcoupon generation parameters include the following:

-   -   (a) Demographic data;    -   (b) Geographic data;    -   (c) Offer size for a coupon offer. This may be specified in the        terms of a minimum offer size and a maximum offer size;    -   (d) The particular medium for which a coupon needs to be        generated. Examples of media include video content, banner ads,        and printed ads.    -   (e) Publisher. Examples of publishers includes Facebook,        YouTube, CNN etc.;    -   (f) Context for the coupon. Examples of contexts includes        sports, politics, science, business, lifestyle, etc.;    -   (g) Psycho-graphic information comprising values, opinions,        attributes, interests, and lifestyles associated with a target        demographic group.

Finally, the use cases 200 include a reporting function 212 wherebyreports are generated for Advertisers and Publishers.

Referring now to FIG. 3 of the drawings, there is shown use cases 300for coupon generation, in accordance with one embodiment of theinvention. In terms of the use cases 300, a Publisher sends a query Q1to the DCPMS 102. The query Q1 is a request for a coupon. Generally, atthe time of sending the query Q1, the Publisher is already publishingcontent to a customer and is the further, typically displaying anadvertisement unit (ad unit) in association with the content. This canbe seen in FIG. 7a , which shows media 700 being published on a customernode 108, wherein the media 700 includes content 702 and an ad unit 704.FIG. 5 shows the elements of the query Q1, in one embodiment. As will beseen, Q1 includes customer information 500 and an ad unit id 502. The adunit id 502 corresponds to the ad unit being shown to the Customer. Thecustomer information corresponds to profile information/data 706 (seeFIG. 8) about the Customer. The profile data 706 is collected from theCustomer node 108 by the Publisher and includes that customer's browsingbehavior and information about the customer device itself.

Responsive to receiving the coupon query Q1, the DCPMS 102 executes aprocess coupon query block 304. Under this block, the DCPMS 102 attemptsto match the ad unit id in the coupon query Q1 in an ad unit list. Thead unit list is provisioned by an Advertiser and is basically a listingof ad units for which coupons must be generated by DCPMS 102. Thus,under the process 304, if the ad unit id is matched then a generatecoupon function 306 is executed. Under this process, a personalizedcoupon is generated based on the coupon configuration parameters andbased on machine learning techniques.

The use cases 300 also include a reply to query function 308 wherein theDCPMS 102 replies to the query Q1 by returning a coupon to the publisher302 or a reply indicating that no coupon is available for the particularad unit associated with the coupon request Q1. FIG. 7B shows the media700 that is published on a customer node 108 as updated by the Publisherto include a coupon 708.

FIG. 4 shows use cases 400 for coupon displaying and clipping on thecustomer node 402, in accordance with one embodiment of the invention.As will be seen, the customer node 108 is configured to display contentby executing a display content function 402. The display contentfunction 402 may be extended to include a display ad function 404 whichin turn may be extended to include a display coupon function 406 if thead unit associated with the ad being displayed is match by the DCPMS102, as described earlier. A profile customer ( ) function 408 collectsprofile information for a customer which is transmitted to thePublisher. The use cases 400 also includes a coupon clipping ( )function 410. Under the coupon clipping function 410, a Customerperforms a ‘clipping action’ in relation to a coupon. For example, inone embodiment, the clipping action may include selection of a clippingbutton associated with the coupon. Responsive to said clipping action,the coupon clipping function 410 generates a coupon clippingnotification and transmits it to the DCPMS 102.

Referring now to FIG. 8 of the drawings, there is shown a process 800executed on the DCPMS 102 responsive to receiving a coupon clippingnotification. At block 802, a check is made to determine if the customeris a registered customer. In one embodiment this step includesvalidating customer credentials included in the coupon clippingnotification. If it is determined that the customer was not registered,then at block 804, a registration process is executed in order toregister the customer. This process may include redirecting a customerto a registration page in order for the customer to input registrationinformation. At block 806, the coupon identified by the coupon id in thecoupon clipping notification is added to the customer's account. At thispoint, the DCPMS 102 may inform the Publisher that the coupon has beenclipped, in which case the publisher may instruct a browser being usedby the customer node 108 to view the coupon to stop displaying thecoupon.

In the case where a Customer is using the coupon app 108B to view thepublished content, the coupon app 108B includes logic to stop showingthe coupon as soon as the coupon clipping action is performed. Thus, aseamless coupon clipping experience is facilitated.

Referring now to FIG. 9A of the drawings, there is shown a use case forcoupon redemption by a Customer. As will be seen, a coupon redemption( )function 900 includes a process 902 for encoding a coupon fortransmission, and a process 904 for transmitting said encoded coupon toa retailer node. In one embodiment, the process 902 for encoding thecoupon for transmission is based on the encoding scheme describe aboveand encodes the coupon as an audio signal which is then transmitted viaa speaker associated with the customer node 108. The retailer node 110then uses a microphone to detect the audio encoding. FIG. 9B also showsa use case for the retailer coupon app 110A to redeem a coupon, inaccordance with one embodiment. Referring to FIG. 9B, process 906comprises a receive coupon id ( ) function whereby a microphone of theretailer node 110 is used to listen for the coupon transmission from thecustomer node 108. A decode coupon id ( ) process 908 decodes the audiosignal in order to extract the coupon id. An authenticate coupon id ( )process 910 includes transmission of the coupon id to the DCPMS 102 bythe retailer coupon app for authentication. The DCPMS 102 authenticatesthe coupon id and returns coupon parameters associated with the couponid that was authenticated. The retailer coupon app then executes areceive coupon parameters ( ) function 912 to receive the couponparameters from the DCPMS 102. A service customer ( ) function 914includes servicing the customer by providing the goods and/or servicesassociated with the coupon. A apply discount ( ) function 916 extendsthe service customer ( ) function 914 to apply the discount indicated inthe coupon to the transaction with the customer. A report redemption ( )function 918 includes operations to report any coupon redemption to theDCPMS 102.

Referring now to FIG. 6 of the drawings, use cases 600 are associatedwith the coupon app 108B. As will be seen, the use cases 600 may includea browse coupons ( ) function 602. This function allows a Customer tobrowse previously clipped coupons. A search coupon ( ) function 604allows the Customer to search for particular coupons based on searchcriteria. A suggest coupon for redemption ( ) function 608 implementsfunctionality to proactively suggest coupons for redemption to aCustomer. For example, in one embodiment based on the location, theCustomer may be shown coupons that are only available for redemption atthat particular location. Finally, the use case 600 includes a redeemcoupon function ( ) 610, whereby the Customer may redeem a selectedcoupon, as has been described above.

Referring now to FIG. 10 of the drawings, there is shown a coupon 1000which is published in association with an advertisement for women's'lipstick. The coupon 1000 is shown in magnified view FIG. 11 of thedrawings. As will be seen, the coupon 1000 includes a discount of $1.25,and a coupon expiration, which is set to 15 days. Further, the coupon1000 includes a ‘clip it button’. This button may be used to clip thecoupon 1000 in accordance with the techniques disclosed herein.

FIG. 12 shows a report 1200 that may be generated for an Advertiser, inaccordance with one embodiment. The report 1200 includes linkinginformation 1202 to link ad unit id, coupon id, customer id, advertiserid, and retailer id. Report 1200 also includes an analytics component1204 which may provide detailed analysis on a coupon's clip rate and itsredemption rate. The coupon clip rate and redemption rate may be used tooptimize a coupon campaign. As has been mentioned, machine runningtechniques are used to generate a coupon in a dynamic fashion. Forexample, coupon may be configured to have a certain clip rate and acertain redemption. If a clip rate for a coupon is too high the systemmay dynamically reduce the discount associated with the coupon in orderto throttle or scale back the redemption rate. Alternatively, if thecoupon clip rate is too low, then the DCPM 102 S may dynamicallyincrease the discount associated with the coupon in order to achieve thedesired clip rate. Likewise, a coupons redemptions rate may be used todynamically scale the offer sized associated with the coupon in order toachieve a desirable redemption rate.

FIG. 13 shows an example of hardware 1300 that may be used to implementthe DCPMS 102 in accordance with one embodiment. The hardware 1300 mayinclude at least one processor 1302 coupled to a memory 1304. Theprocessor 1302 may represent one or more processors (e.g.,microprocessors), and the memory 1304 may represent random access memory(RAM) devices comprising a main storage of the hardware, as well as anysupplemental levels of memory e.g., cache memories, non-volatile orback-up memories (e.g. programmable or flash memories), read-onlymemories, etc. In addition, the memory 1304 may be considered to includememory storage physically located elsewhere in the hardware, e.g. anycache memory in the processor 1302, as well as any storage capacity usedas a virtual memory, e.g., as stored on a mass storage device.

The hardware also typically receives a number of inputs and outputs forcommunicating information externally. For interface with a user oroperator, the hardware may include one or more user input output devices1306 (e.g., a keyboard, mouse, etc.) and a display 1308. For additionalstorage, the hardware 1300 may also include one or more mass storagedevices 410, e.g., a Universal Serial Bus (USB) or other removable diskdrive, a hard disk drive, a Direct Access Storage Device (DASD), anoptical drive (e.g. a Compact Disk (CD) drive, a Digital Versatile Disk(DVD) drive, etc.) and/or a USB drive, among others. Furthermore, thehardware may include an interface with one or more networks 1312 (e.g.,a local area network (LAN), a wide area network (WAN), a wirelessnetwork, and/or the Internet among others) to permit the communicationof information with other computers coupled to the networks. It shouldbe appreciated that the hardware typically includes suitable analogand/or digital interfaces between the processor 1312 and each of thecomponents, as is well known in the art.

The hardware 1300 operates under the control of an operating system1314, and executes application software 1316 which includes variouscomputer software applications, components, programs, objects, modules,etc. to perform the techniques described above.

In general, the routines executed to implement the embodiments of theinvention, may be implemented as part of an operating system or aspecific application, component, program, object, module or sequence ofinstructions referred to as “computer programs.” The computer programstypically comprise one or more instructions set at various times invarious memory and storage devices in a computer, and that, when readand executed by one or more processors in a computer, cause the computerto perform operations necessary to execute elements involving thevarious aspects of the invention. Moreover, while the invention has beendescribed in the context of fully functioning computers and computersystems, those skilled in the art will appreciate that the variousembodiments of the invention are capable of being distributed as aprogram product in a variety of forms, and that the invention appliesequally regardless of the particular type of machine orcomputer-readable media used to actually effect the distribution.Examples of computer-readable media include but are not limited torecordable type media such as volatile and non-volatile memory devices,USB and other removable media, hard disk drives, optical disks (e.g.,Compact Disk Read-Only Memory (CD ROMS), Digital Versatile Disks,(DVDs), etc.), flash drives among others.

The invention claimed is:
 1. A method for redeeming a coupon using amobile device, comprising: allowing a user to select the coupon;accessing at least one melody stored in a memory of the mobile device;passing a coupon identifier for the coupon and the at least one melodyto an encoder component of the mobile device; sandwiching the couponidentifier between two portions of the melody to generate a bookendmelody; encoding the bookend melody by the encoder component to generatea signal for square wave transmission; and transmitting said signalthrough a speaker of said mobile device for reception through amicrophone of a receiving mobile device.
 2. The method of claim 1,wherein accessing at least one bookend melody comprises accessing twomelodies designed, when encoded, to bookend the encoding correspondingto the coupon identifier so that said encoding corresponding to thecoupon identifier is sandwiched between the encodings corresponding tothe two melodies.
 3. The method of claim 1, wherein the at least onebookend melody is selected to mask the encoding corresponding to thecoupon identifier during transmission of the signal.
 4. The method ofclaim 1, wherein said signal is a first signal.
 5. The method of claim4, further comprising generating a second signal and transmitting sametogether with the first signal; wherein the second signal has lowerautocorrelation properties and is selected to trigger the second deviceto invoke an expensive filter, as measured in terms of one of power,processing; and memory usage, to search for the second signal.
 6. Themethod of claim 1, wherein a waveform corresponding to the signal has aconstant envelope.
 7. The method of claim 1, wherein the signalcomprises a quasi-periodic signal with a frequency that increases at aconstant rate in time over a specified band.
 8. A mobile device,comprising: a memory to store at least one melody and a couponidentifier; an encoder for encoding at least one bookend melody togenerate a square wave signal for transmission, wherein the bookendmelody is generated by sandwiching the coupon identifier between twoportions of the melody; and a speaker to transmit said signal forreception through a microphone of a receiving mobile device.
 9. Themobile device of claim 8, wherein the encoder is configured to encodetwo melodies designed, when encoded, to bookend the encodingcorresponding to the coupon identifier so that said encodingcorresponding to the coupon identifier is sandwiched between theencodings corresponding to the two melodies.
 10. The mobile device ofclaim 8, wherein the at least one bookend melody is selected to mask theencoding corresponding to the coupon identifier during transmission ofthe signal.
 11. The mobile device of claim 8, wherein said signal is afirst signal.
 12. The mobile device of claim 11, further configured togenerate a second signal and to transmit same together with the firstsignal; wherein the second signal has lower autocorrelation propertiesand is selected to trigger the second device to invoke an expensivefilter, as measured in terms of one of power, processing; and memoryusage, to search for the second signal.
 13. The mobile device of claim8, wherein a waveform corresponding to the signal has a constantenvelope.
 14. The mobile device of claim 8, wherein the signal comprisesa quasi-periodic signal with a frequency that increases at a constantrate in time over a specified band.